The phrasal you are thinking about could be hutch up. This is described as an idomatic phrase meaning
To move slightly (sideways), in order to make room for someone; for example to move in a bed to make room for someone else to lie, or to move sideways on on a seat so as to allow someone room to sit and share that same seat.
Although it is defined as moving over to make room for someone it often involves two or more people moving closer together on a seat in order to create the space as in "Hutch up you two, make room for a little one." The phrase is idiomatic rather than formal English and is not often used with strangers, its use does, usually, imply some degree of intimacy with the person or people addressed. I'm British and I accept that "hutch up" may not be used for "move over" the US but it may still be the phrase you're looking for.
According to the Wikipedia page "hutch up" can also mean to share a home with someone so that the rent is more affordable and to put on a more heterosexual attitude to be more socially acceptable but its "move over" meaning is much more familiar to me and is, I suspect, the original.